The invention relates to a seated valve as disclosed in the preamble of claim 1.
As known from DE-U-298 10 860, FIG. 4, in a seated valve formed as a {fraction (3/2)}-ways seated valve with solenoid actuation, the closure element co-acting with the valve seat at the side of the actuator is a full sphere made of steel. Full spheres allow to achieve an absolutely leakage-free closing position between the spherical sealing surface of the closure element and the circular valve seat and in addition are available in different sizes and for fair costs. The diameter of the valve seat is dictated by the requirements valid for the seated valve, e.g. the maximum through flow rate and the allowed through flow resistance at maximum through flow rate. The radius of the spherical sealing surface of the closure element has to be matched with the diameter of the valve seat in order to assure an optimum co-action between both. On the other hand, it is intended to keep the interior guiding and sealing diameter of the cylindrical bushing as small as possible, about coinciding to the diameter of the valve seat, in order to maintain the forces moderately resulting from the pressure behind the closure element and acting on the actuator as well as the actuation force for adjustments of the closure element against the valve seat. The sphere diameter of a fair cost full sphere used as the closure element is in contradiction to said intention, because said full sphere diameter is considerably larger than the diameter of the valve seat. For this reason, the cylindrical bushing inner bore conventionally has a widened portion receiving the full sphere in the region between the actuator and the valve seat. Said widened portion requires to insert the full sphere closure element into the seated valve already together with said cylindrical bushing. The closure element then remains captured within said widened portion. In view to a simple and fair cost manufacturing of the housing bore and the cylindrical bushing, and also for mounting reasons, the cylindrical bushing conventionally is pressed into the housing bore and is secured in place by mortising the outer side of the housing around the opening of said housing bore. Said securing in place by mortising cannot be released without damage. When forming and mounting the valve seat within the housing bore and during the assembly of the cylindrical bushing the circular edge of the valve seat may be damaged or deformed which is detrimental for the leakage-free co-action between the spherical sealing surface of the closure element and the valve seat. Even other influences may deteriorate the roundness of the valve seat or the preciseness of a tapered chamfer of the valve seat, e.g. corrosion. Finally, after long time operation of the seated valve the leakage-free co-action may suffer from impacts occurred or wear. In all said cases a subsequent treatment of the valve seat is no longer possible due to the full sphere captured within said cylindrical bushing without destroying the cold flow formation used to position the cylindrical bushing in place.
Further prior art related to seated valves having centreless ground spheres used as closure elements can be found in DE-U-295 13 944.
It is an object of the invention to create a seated valve of the kind as disclosed above in which a necessary subsequent treatment of the valve seat at its side facing towards the actuation means can be made possible and for which the advantage of a simple manufacturing and mounting and the method of cold flow deformation when positioning the cylindrical bushing remains.
Said object can be achieved by the features of claim 1.
Even though the closure element by its spherical sealing surface optimally co-acts with the circular valve seat (no leakage in the closing position), thanks to the waist portion the closure can be inserted at any time into the already positioned cylindrical bushing or can be removed therefrom and the inner guiding and sealing diameter of the cylindrical bushing can be dimensioned as small as possible. It is possible at any time to carry out a subsequent treatment of the valve seat without destroying cold flow deformation positioning the cylindrical bushing. In addition, by said waist portion a proper guidance of the closure element within the inner bore of the cylindrical bushing is achieved so that the frequently occurring dancing of a full sphere closure element is prevented which not only generates loud noises but also significant wear. The waist portion of the closure element made from a fair cost full sphere with moderate efforts and very accurately allows to insert and remove it easily.
The diameter of the waist portion of the closure element ought to be slightly smaller than the inner guiding and sealing diameter of the cylinder bushing in order to guarantee an unobstructed operation movement of the closure element and its easy removal or insertion.
It is expedient for the manufacturing when the inner sealing and guiding diameter of the cylindrical bushing remains uniform along its longitudinal extension or if it increases by at least one step towards the outer side. Said step could be located at the end region of the cylindrical bushing facing the outer side of the housing and allows to place a closure ring there. The smallest inner diameter of the cylindrical bushing is provided where the closure element is to be received.
Expediently the waist portion of the closure element is ground cylindrically in order to achieve a proper guiding of the closure element. For grinding the full sphere expediently a centreless-grinding process is applied. In a centreless grinding process a driven cylindrical grinding disk is situated vis-à-vis to an also driven cylindrical driving disk with an intermediate distance varied by adjusting both disks towards each other. Into the intermediate space between said disks one full sphere or several full spheres are placed side by side supported by a guiding rod. No further auxiliary devices are required. Such a grinding run lasts only a few tenths of a second, e.g., for an 8 mm full sphere made of hardened steel.
Alternatively, said waist portion could be formed by a circumferential groove (e.g. machined on a lathe) resulting from a chipping or grinding process.
The diameter of the waist portion of the closure element should lie between about 75% and 90% of the full sphere diameter.
For manufacturing and mounting it is of advantage to form the valve seat at an insert pressed into the bore of the housing. When pressing in said insert or for the reasons mentioned above the valve seat, e.g. in use, may lose its circular shape, however, prior to inserting the closure element or after removal of the closure element the valve seat in place can be subsequently treated accordingly. It is then of secondary importance whether the cylindrical bushing is abutting said insert with axial pressure or not, because such subsequent treatment will remedy any deformation of the valve seat. It is to be noted that such a subsequent treatment can be made in the already final operating position of the cylindrical bushing and the insert.
In order to secure the cylindrical bushing in place by cold flow deformation in the simplest way the outer side of the housing surrounding the end of the cylindrical bushing is mortised. This further leads to an efficient sealing effect.
The diameter of the full sphere should be about 125% and the diameter of the waist portion about 113% of the diameter of the valve seat.
The push rod of the actuator at which the actuating forces are acting and which has to be sealed towards the exterior should have a diameter which is about 60% of the diameter of the valve seat.
In order to use a single closure element type in a certain seated valve type even if this type contains several co-operating valve units, another closure element situated at the spring loaded side opposite to the actuator side should be of the same form and size as the closure element at the actuating side.